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[KeelsonGraham]

A strange one. I have a set of 4 lead acid golf cart batteries paralleled to give me about 360 ah at 12v. A couple of weeks ago the low volt alarm sounded on my Victron battery monitor, even though the calculated charge capacity was showing 97%. The boat’s voltmeters were showing in the yellow range.

The batteries are less than a year old and I’ve never let the electrolyte levels fall.

Any ideas?

[Jim Hardesty]

Sounds like bad, probably shorted, cell in one of the batteries.  Isolate each battery and check voltage, think you'll find one battery that reads less than 11 volts.  One bad battery will suck the power out of the good battery.
Jim

[Stu Jackson]

kg,  what did the voltage AT THE BATTERY BANK(S) read?  Saying "The boat’s voltmeters were showing in the yellow range" is meaningless, too, to anybody else.

[Ron Hill]

Keel : Do as Jim suggested. Check the voltage at each battery separately!!

A thought

[Paulus]

I checked my golf cart batteries last week.  I have 4 golf cart batteries, disconnected all of them.  Checked each cell with a hydrometer and also a volt meter.
Hope this is helpful
Paul

[KeelsonGraham]

Thanks guys, I’ll do that.

[Dave Spencer]

Keelson,
It's also important to understand exactly what your Victron is telling you.  100% capacity of your batteries is whatever you tell the Victron is 100%.  There are lots of postings on the subject of battery capacity as measured by battery monitors on this site.  Here's a starting point.  https://c34.org/bbs/index.php/topic,11555.msg93342.html#msg93342
A bad cell in one battery is a good possibility, but, unless you know exactly how the Victron was set up, it's also possible that the batteries were simply allowed to become discharged if you are relying on the "Percent State of Charge" reading on the Victron to assess their status.  (do you have solar or a 120V battery charger?)

Good luck with your detective work!

[KeelsonGraham]

it's also possible that the batteries were simply allowed to become discharged if you are relying on the "Percent State of Charge" reading on the Victron to assess their status.  (do you have solar or a 120V battery charger?)

Good luck with your detective work!

Wow, yes I am relying on percent SOC! After installing the new batteries last year I charged them fully and then set the Victron to 100% for the appropriate battery capacity. Since then, I’ve relied solely on the SOC, rather than voltage, to assess when to do a re-charge. This strategy worked fine doing a 5-day Biscay crossing when we switched the engine on as required to maintain SOC between 60-80%. Over winter the SOC never fell below 97% so I did no re-charging. Sounds like I might be doing it all wrong.